Cooling systems and methods using single-phase fluid

ABSTRACT

A cooling system includes a heat exchanger having one or more rows of multiple flat tubes, louvered fins disposed between pairs of flat tubes, and special header tube connections to form a counter flow heat exchanger. Heat exchangers having multiple rows may be placed near or close to the server racks and may be in fluid communication with an outdoor heat exchanger having one or more rows. A single-phase fluid is pumped through a fluid circuit or loop, which includes the heat exchangers at the server racks and the outdoor heat exchanger. The single-phase fluid circuit including the heat exchangers at the IT racks may alternatively be in thermal communication with a water circuit that includes an outdoor fluid cooler. The flat tubes can be formed tubes with one or more channels, or extruded tubes with multiple channels. The heat exchangers include header tubes/connections, which facilitate easy fabrication and connection between rows and inlet/outlet, and lower the pressure drop.

BACKGROUND Technical Field

The present disclosure relates to cooling systems and methods usingsingle-phase fluid.

Description of Related Art

Over the past several years, computer equipment manufacturers haveexpanded the data collection and storage capabilities of their servers.The expansion of server capabilities has led to an increase in totalpower consumption and total heat output per server and per server rackassembly in data centers. It has also led to an increase in power andtemperature control requirements for computer data collection andstorage. As a result, the data collection and storage industry hassought and is seeking new, innovative equipment, systems, and designstrategies to handle the tremendous and continued growth in capacity ofcomputer data collection and storage.

Cooling systems for computer server racks have been struggling to keeppace with the ability to cool ever increasing computer server heat loadsin data centers. The increase of computer server heat loads (measured inkilowatts (kW)) has required that more space be allotted for the coolinginfrastructure within the data rooms or that the cooling systems areconcentrated at the heat source, i.e., the computer server racks.Recently, cooling systems have been designed to concentrate the coolingat the computer server racks. These cooling systems include rear-doorheat exchangers and rack-top coolers.

SUMMARY

In one aspect, the present disclosure features a system for cooling aplurality of information technology (IT) racks. The system includes aheat exchanger disposed at or near a hot aisle formed by the pluralityof IT racks. The heat exchanger, in turn, includes a first row includinga first plurality of flat tubes and a second row including a secondplurality of flat tubes in fluid communication with the first row. Thesystem further includes a fan disposed in air communication with theheat exchanger. The fan moves air from the hot aisle through the heatexchanger from the second row to the first row. The system furtherincludes a single-phase fluid circuit coupled to and in fluidcommunication with the heat exchanger. The single-phase fluid circuitcirculates a single-phase fluid through the heat exchanger from thefirst flat tube to the second flat tube.

In aspects, each flat tube of the first and second plurality of flattubes includes one or more channels. Each flat tube of the first andsecond plurality of flat tubes includes two channels, three channels, orfive channels.

In aspects, each flat tube of the first and second plurality of flattubes is an extruded or brazed aluminum tube.

In aspects, the system includes a plurality of fins disposed betweenpairs of flat tubes of the first and second plurality of flat tubes. Inembodiments, each of the plurality of fins may include a wave pattern inthe direction of air flow. In embodiments, the plurality of fins is alouvered fin.

In aspects, the heat exchanger further includes a third row including athird plurality of flat tubes in fluid communication with the secondrow; and a fourth row including a fourth plurality of flat tubes influid communication with the third row. In aspects, the fan moves hotair from the hot aisle through the heat exchanger from the fourth row tothe first row, and the single-phase fluid circuit circulates thesingle-phase fluid through the heat exchanger from the first row to thefourth row.

In aspects, the first row and the second row are connected through anO-ring using one or more fasteners, such as bolts or screws.

In aspects, the single-phase fluid is a fluoroketone (FK) fluid. Inaspects, the FK fluid includes micro-encapsulated, phase changematerial.

In aspects, the system further includes a water circuit; and a secondheat exchanger coupled between the single-phase fluid circuit and thewater circuit.

In aspects, the system further includes a third heat exchanger disposedin an outdoor fluid cooler and in fluid communication with the watercircuit. The third heat exchanger includes one or more rows of aplurality of flat tubes.

In aspects, the system further includes a second heat exchanger disposedin an outdoor fluid cooler and in fluid communication with thesingle-phase fluid circuit. The second heat exchanger includes one ormore rows of a plurality of flat tubes.

In aspects, the heat exchanger is disposed above the hot aisle.

In aspects, the system further includes an air duct coupled between theheat exchanger and the hot aisle.

In another aspect, the present disclosure features a method for coolinga plurality of information technology (IT) racks. The method includes:moving air from a hot aisle formed by a plurality of IT racks across afirst plurality of flat, aluminum-formed tubes of a first row of a firstheat exchanger and then across a second plurality of flat,aluminum-formed tubes of a second row of the heat exchanger; pumping asingle-phase fluid through the heat exchanger from the second pluralityof flat, aluminum-formed tubes to the first plurality of flat,aluminum-formed tubes to transfer heat from the air to the single-phasefluid, and through a first channel of a second heat exchanger; andcirculating a cooling water solution through a second channel of thesecond heat exchanger.

In aspects, the single-phase fluid is a fluoroketone (FK) fluid. Inaspects, the FK fluid includes micro-encapsulated, phase changematerial.

In still another aspect, the present disclosure features a heatexchanger. The heat exchanger includes a first row including a firstpair of header tubes and a first plurality of flat tubes coupled betweenthe first pair of header tubes so that the first plurality of flat tubesare in fluid communication with the first pair of header tubes. The heatexchanger also includes a second row including a second pair of headertubes and a second plurality of flat tubes coupled between the secondpair of header tubes so that the second plurality of flat tubes are influid communication with the second pair of header tubes. The headertube of the first pair of header tubes is coupled to a header tube ofthe second pair of header tubes without using a brazing process. Theheat exchanger also includes a plurality of fins disposed between eachpair of the first and second plurality of flat tubes.

In aspects, the first row and the second row are separately constructedusing a brazing process. In aspects, the first and second plurality offlat tubes each include two channels, three channels, or five channels.In aspects, the first and second plurality of flat tubes are extruded orbrazed aluminum tubes.

In aspects, each of the plurality of fins include a wave pattern in thedirection of air flow. In aspects, the plurality of fins is a louveredfin.

In aspects, the heat exchanger includes a fluid inlet coupled to and influid communication with the first row, a fluid outlet coupled to and influid communication with the second row, and one or more fans configuredto move hot air through the heat exchanger from the second row to thefirst row.

In aspects, the header tube of the first pair of header tubes is coupledto the header tube of the second pair of header tubes by coupling aheader connection of the header tube of the first pair of header tubesto a header connection of the header tube of the second pair of headertubes via an O-ring or a gasket using a fastener, such as one or morebolts or screws.

In still another aspect, the present disclosure features a method ofmanufacturing a heat exchanger. The method includes coupling a firstplurality of flat tubes between a first pair of header tubes through anautomatic brazing process so that the first plurality of flat tubes arein fluid communication with the first pair of header tubes; coupling asecond plurality of flat tubes between a second pair of header tubesthrough an automatic brazing process so that the second plurality offlat tubes are in fluid communication with the second pair of headertubes; and coupling a first header tube of the first pair of headertubes to a second header tube of the second pair of header tubes withoutusing a brazing process.

In aspects, method of manufacturing further includes coupling the firstheader tube to the second header tube by coupling a first headerconnection of the first header tube to a second header connection of thesecond header tube through an O-ring or a gasket.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and features of the present disclosure are describedhereinbelow with references to the drawings, wherein:

FIG. 1 is a schematic diagram illustrating a single-phase fluid coolingsystem in accordance with an embodiment of the present disclosure;

FIG. 2 is a schematic diagram illustrating a single-phase fluid coolingsystem with an intermediate heat exchanger in accordance with anotherembodiment of the present disclosure;

FIG. 3 is a schematic diagram illustrating a single-phase fluid coolingsystem with an intermediate heat exchanger and individual pump/pipeloops in accordance with yet another embodiment of the presentdisclosure; and

FIGS. 4A and 4B are schematic diagrams illustrating a cooling systemwith hot air return to rooftop air handler, in accordance with stillanother embodiment of the present disclosure.

FIG. 5A is a front view of a heat exchanger provided in accordance withthe present disclosure;

FIG. 5B is a cross-sectional view of the heat exchanger of FIG. 5A takenalong section line 5A-5A of FIG. 5A;

FIG. 5C is a top view of the heat exchanger of FIG. 5A;

FIG. 5D is a cross-sectional view of the heat exchanger of FIG. 5A takenalong section line 5D-5D of FIG. 5C;

FIG. 6 is a top view of another heat exchanger provided in accordancewith the present disclosure;

FIG. 7A is a front view of yet another heat exchanger provided inaccordance with the present disclosure;

FIG. 7B is a cross-sectional view of the heat exchanger of FIG. 7A takenalong section line 7A-7A of FIG. 7A;

FIG. 7C is a side view of the heat exchanger of FIG. 7A;

FIG. 8A is a front view of yet another heat exchanger provided inaccordance with the present disclosure;

FIG. 8B is a top view of the heat exchanger of FIG. 8A;

FIG. 8C is a cross-sectional view of a flat tube of the heat exchangerof FIGS. 8A and 8B taken along section line 8C-8C of FIG. 8B;

FIG. 9A is a top view of heat exchanger fins provided in accordance withsome embodiments of this disclosure;

FIG. 9B is a front view of the heat exchanger fins of FIG. 9B;

FIG. 10A is a detailed front view of the heat exchanger fins of FIGS. 9Aand 9B in accordance with some embodiments of this disclosure;

FIG. 10B is a cross-sectional view of a heat exchanger fin of FIG. 10Ataken along section line 10B-10B of FIG. 10A;

FIG. 11A is a top view of yet another heat exchanger provided inaccordance with some embodiments of the present disclosure;

FIG. 11B is a front view of the heat exchanger of FIG. 11A;

FIG. 11C is a left side view of the heat exchanger of FIGS. 11A and 11B;

FIG. 11D is a right side view of the heat exchanger of FIGS. 11A and11B;

FIG. 12 is a flow diagram illustrating a process according toembodiments of the present disclosure; and

FIG. 13 is a flow diagram illustrating a method of manufacturingaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are now described in detail withreference to the drawings in which like reference numerals designateidentical or corresponding elements in each of the several views. In thedrawings and in the description that follows, terms such as front, rear,upper, lower, top, bottom, and similar directional terms are used simplyfor convenience of description and are not intended to limit thedisclosure. Additionally, in the following description, well-knownfunctions or constructions are not described in detail to avoidobscuring the present disclosure in unnecessary detail.

Some computer servers now produce high heat, and rear-door heatexchangers and other similar cooling products on the market havedifficulty handling the cooling requirements of these high-densitycomputer servers. Also, traditional fin-copper-tube coils producesignificant air side and fluid side pressure drop while single-rowflat-tube or microchannel heat exchangers produce high temperatureapproach for single-phase fluid, resulting in compromised performance.

The present disclosure is related to systems and methods for cooling adata center or other heat load having a high temperature difference.Compared to existing pumped R134a liquid refrigerant systems, thesystems according to embodiments of the present disclosure utilize thelow specific heat and high temperature difference of a fluoroketone (FK)fluid and counter-flow heat exchangers to achieve higher energyefficiency. The heat exchanger and other portions of the cooling systemare less likely to leak due to the FK fluid's low working pressure andsingle-phase nature. Also, the FK fluid has a global warming potential(GWP) of only one whereas R134a has a GWP of approximately 1400.Compared to water-based liquid cooling systems, the systems according tothe present disclosure are safer because FK fluid does not harm serverelectronics if a leak occurs, there is no possibility of freezing in lowtemperature outdoor ambient conditions, and there are no concerns aboutcorrosion compared to water-based systems.

The cooling systems according to embodiments of the present disclosureuse a single-phase fluid. For example, the cooling systems may use an FKfluid (e.g., Novec™ 649 made by 3M™) or a heat transfer fluid withsimilar properties. As another example, the cooling systems may use aHydrofluoroether (HFE) fluid, which is a non-ozone-depleting fluid. Thesingle-phase fluid is pumped to heat exchangers closely coupled toserver racks or another heat load to provide cooling. The single-phasefluid warmed by the computer server racks or another heat load is thenpumped to an outdoor fluid cooler to reject heat to ambient directly for“free cooling” and further cooled (if necessary) through a chillerevaporator to the needed or desired supply temperature (e.g., 16.7° C.).The cooled single-phase fluid is pumped back to the heat exchangers nearthe server racks to complete the cycle. The single-phase fluid can alsobe any other liquid fluid that is non-conductive and inert.

Further, compared to a pumped liquid refrigerant system, the fluidsystem according to embodiments of the present disclosure does not use afluid that changes from a liquid phase to a vapor phase and works underrelatively low pressure, and thus is much more robust to operate. Alsothe fluid cycle according to embodiments of the present disclosuremaintains high temperature change (e.g., between the temperature of thefluid leaving the heat exchangers at the server load and the temperatureof the fluid being supplied by the chiller and/or outdoor fluid cooler)and low temperature approach resulting in a lower fluid flow rate,higher energy efficiency, and more “free cooling” or partial “freecooling” hours than other cooling loop systems.

The present disclosure also features heat exchangers having multiplerows of tubes, and special header tubes to maintain counter flow andfacilitate easy connection between rows and inlet/outlet.

FIG. 1 shows a schematic diagram of a cooling system 100 includingmultiple cooling modules 110. Hot air from IT racks 112 is discharged tothe hot aisles 114 and then drawn into FK fluid heat exchangers 116 ofthe cooling modules 110 at the top of the hot aisles by fans 118 of thecooling modules 110. The heat exchangers 116, which are described inmore detail below, include multiple rows of multiple flat tubes. Forexample, the heat exchangers 116 may include two, three, four, five, orsix rows of multiple flat tubes depending on the cooling requirements ofthe IT racks 112. The hot air is cooled by FK fluid flowing through heatexchangers 116, or another appropriate single-phase fluid, on the tubeside of the heat exchangers 116 and the cooled air is discharged back tothe room or cold aisle. The warmed FK fluid from the heat exchangers 116is pumped by a pump 120 to fluid-to-air, free-cooling heat exchanger 142of an outdoor fluid cooler 140 where the FK fluid is cooled by ambientair.

The heat exchanger 142 includes one or more rows of flat tubes. Forexample, the heat exchanger 142 may include one or two rows of multipleflat tubes. In another example, the heat exchanger 142 may include tworows of multiple flat tubes in a counter-flow configuration. If furthercooling of the FK fluid is needed because, for example, of the hightemperature of the ambient air, the modular chiller 130 may be operated.Examples of the modular chiller 130 and the fluid cooler 140 and theiroperation are described in commonly-owned U.S. application Ser. No.15/398,512 titled “System and Methods Utilizing Fluid Coolers andChillers to Perform In-Series Heat Rejection and Trim Cooling,” theentire contents of which are incorporated by reference herein.

In one example method, if the temperature of the FK fluid, or anotherappropriate single-phase fluid, leaving from the fluid cooler 140reaches a needed supply temperature (e.g., 16.7° C.) when ambient air iscool enough (e.g., 13.3° C.), the FK fluid is pumped back to the indoorhot aisle heat exchangers 116 to complete the cycle for full “freecooling” (no compressor or chiller operation is needed, e.g., themodular chiller 130 does not need to be operated). If the FK fluidleaving from the fluid cooler 140 is greater than the needed supplytemperature (e.g., 16.7° C.), the chiller 130 is operated to furthercool the FK fluid flowing through the chiller 130 (e.g., flowing throughthe evaporator of the chiller 130) to the setpoint. Then, the furthercooled FK fluid is pumped back to the indoor hot aisle heat exchangers116 to complete the cycle as “partial free cooling”. Adiabatic wet media144, over which water is distributed by a media water distributionsystem 146, or a water spray can be placed at the air inlet of the fluidcooler 140 to cool the entering air temperature to close to the wet bulbtemperature and thereby increase the full free cooling or partial freecooling to save energy.

FIG. 2 illustrates a cooling system 200, according to another embodimentof the present disclosure. An intermediate plate heat exchanger 210 isused to thermally couple the FK fluid loop or circuit 205 near theserver racks to a water loop or circuit 215, which uses cooling water(or a glycol/water mixture or another water solution) to cool the FKfluid and reject heat to the outdoor fluid cooler 140 and/or the chiller130 (when needed). The advantage of this configuration is that the FKfluid charge volume can be significantly reduced.

FIG. 3 illustrates a cooling system 300 according to yet anotherembodiment of the present disclosure. An intermediate plate heatexchanger 310 is used to thermally couple the FK fluid loop 305 near theIT racks to a water loop 315, which uses cooling water (or aglycol/water mixture or another water solution) to cool the FK fluid andreject heat to the outdoor fluid cooler 140 and chiller 130 (whenneeded). The cooling system 300 uses small secondary pumps 308 and pipesto pump the FK fluid to each individual heat exchanger 116 at the hotaisle separately, thus avoiding large liquid supply and return pipes andavoiding influencing other heat exchangers 116 if one fails.

FIGS. 4A and 4B illustrate a cooling system 400 according to stillanother embodiment of the present disclosure. Hot air from the hot aisleis drawn through a duct 402 to a rooftop air handler unit 410 where itis cooled and sent back to the room or cold aisle via a duct 408. Thechilled liquid (e.g., the FK liquid fluid or other similar fluid) ispumped through a single-phase fluid circuit 405, which includes the heatexchanger 415 of the air handler 410 and a heat exchanger 420 (e.g., aflat-plate heat exchanger) that is in fluid communication with theoutdoor fluid cooler 440 and the chiller 430 (via a water circuit 425)to provide cooling for the air handler 410 and reject heat to the fluidcooler 440 and the chiller 430. In some embodiments, the chiller circuit435 of the chiller 430 may utilize a single-phase fluid, such as an FKfluid, or a refrigerant, such as R134a. The heat exchanger 415 and thefree cooling coil of the outdoor fluid cooler 440 may be flat-tube heatexchangers including one or more rows of multiple flat tubes accordingto embodiments disclosed herein, e.g., FIGS. 5A-11D.

According to embodiments of the cooling system, micro-encapsulated,phase-change material (MEPCM) may be added to the liquid FK fluid toincrease heat capacity (i.e., increase the thermal mass/heat transfer)and lower the flow rate/pumping power for all the cooling systems inFIGS. 1-4B. The MEPCM includes multiple different chemical compositionstailored for the working temperature range for data center cooling orany other applications.

In embodiments, the cooling system utilizes amulti-row-flat-aluminum-tube-counter-flow heat exchanger for the indoorhot aisle heat exchanger (or air handler heat exchanger) and outdoorfluid cooler. The high efficiency counter flow heat exchanger can makethe leaving fluid temperature from the indoor heat exchanger close tothe hot air entering temperature, and the air leaving temperature fromthe outdoor fluid cooler close to the entering FK fluid temperature. Putanother way, these heat exchangers have very high number of transferunits (NTU) or high effectiveness (e.g., 95% or higher). This improvesthe system energy efficiency over an R134a pumped liquid system or othercompeting technologies.

FIG. 5A shows a front view of a heat exchanger 500 and FIG. 5B shows across-sectional view of the heat exchanger 500 taken along section line5B-5B of FIG. 5A. The heat exchanger 500 has four rows 501: a first row501 a, a second row 501 b, a third row 501 c, and a fourth row 501 d.Alternatively, the heat exchanger 500 may have two rows or any number ofrows depending on the specific application. Each of the rows 501includes multiple tubes 502: the first row 501 a includes multiple tubesincluding tube 502 a, the second row 501 b includes multiple tubesincluding tube 502 b, the third row 501 c includes multiple tubesincluding tube 502 c, and the fourth row 501 d includes multiple tubesincluding tube 502 d.

The tubes 502 may be flat tubes. The flat tubes may be flataluminum-formed tubes. Each tube 502 may have a single channel, twochannels, or multiple channels (not shown). The tubes 502 may also bemulti-port extruded aluminum tubes. The louver fin (not shown) is usedon the airside 504 (the fins can be stacked with each piece to cover allfour rows 502 a, 502 b, 502 c, 502 d, or each row 502 a, 502 b, 502 c,502 d has its own fins so the fins are separated for each row 502 a, 502b, 502 c, 502 d). The four rows 501 a, 501 b, 501 c, 501 d form acounter flow circuit—liquid fluid enters the fourth row 501 d, thenpasses through the third row 501 c, then passes through the second row501 b, and then exits from the first row 501 a, while airflow enters thefirst row 501 a and leaves from the fourth row 501 d.

Compared to traditional fin-copper-tube coils, the flat tube heatexchanger 500 has better heat transfer performance but lower airflowpressure drop and lower fluid-side pressure drop. Compared to commonflat-tube, cross-flow heat exchangers, the multi-rows and counter-flowcircuiting of the heat exchanger 500 results in high heat-transferefficiency with smaller temperature approach between the liquid and air.This is achieved by the entering header tube 506 a, intermediate headertube 506 b, and exit header tube 506 c of the heat exchanger 500.

FIG. 5B shows a header tube 506 at each end of the heat exchanger 500 tocover all four rows 501 a, 501 b, 501 c, 501 d of flat tubes 502 a, 502b, 502 c, 502 d to form counter-flow circuiting with internalpartitions.

FIG. 5C is a top view of the heat exchanger of FIG. 5A and FIG. 5D is across-sectional view of the heat exchanger of FIG. 5A taken alongsection line 5D-5D of FIG. 5C. As shown in FIG. 5C, a fluid inlet tube508 a is connected to the fourth row 501 d so that the fluid inlet tube508 a is in fluid communication with the flat tubes 502 d of the fourthrow 501 d, and a fluid outlet tube 508 b is connected to the first row501 a so that the fluid outlet tube 508 b is in fluid communication withthe flat tubes 502 a of the first row 501 a. In embodiments of thepresent disclosure, the fluid inlet tube 508 a and the fluid outlet tube508 b may be connected to a single-phase fluid circuit.

FIG. 5D illustrates the multiple flat tubes 502 a-502 d in each of therows 501 a-501 d, respectively. Fins 503 a-503 d are disposed betweenpairs of the flat tubes 502 a-502 d. In some embodiments, the fins 503a-503 d are louvered fins.

FIGS. 6-7C show different embodiments of the rows 501 and header tubes506. FIG. 6 shows two two-row heat exchangers 600 stacked together toform a four-row heat exchanger 610. The connection between the secondrow 602 b and the third row 602 c is through two short connection tubes612, one connection 612 at each end of the header tube (not shown), orone short connection 612 at either end of the header tube. The liquidfluid enters the fourth row 602 d and exits from the first row 602 afrom one end of the header tube 606 of the respective row 602.

FIGS. 7A-7C show four separate rows 602 stacked together to form asingle heat exchanger 610, and liquid connection 614 between every tworows 602 and inlet 614 a and outlet 614 b is through a set of additionalconnection tubes 616 from the other side. FIG. 7C is a left side viewshowing the liquid entrance 614 a, exit 614 b, and transition 616 fromthe second row 602 b to the third row 602 c. The connections 614 betweenthe first row 602 a and the second row 602 b, and between the third row602 c and the fourth row 602 d are similar.

In general, the embodiments of the heat exchangers 500, 610 of thepresent disclosure may be used in any liquid-to-gas heat exchanger. Forexample, the embodiments of the heat exchangers 500, 610 of the presentdisclosure may be used for close-coupling heat exchangers near serverracks in data center cooling, and also for outdoor fluid coolers fordata centers.

FIGS. 8A and 8B illustrate a row of a heat exchanger according toanother embodiment. The row includes multiple flat tubes 801 coupledbetween header tubes 805 a, 805 b. The flat tubes 801 may be aluminumtubes, e.g., extruded aluminum tubes. The row also includes headerconnectors 810 a, 810 b for connecting to one or more other rows. Forexample, header connectors 810 a may connect to header connectors on afirst other row and header connectors 810 b may connect to headerconnectors on a second other row. The header connectors 810 a, 810 b mayattach or connect to header connectors on other rows via an O-ring orgasket using one or more fasteners, such as bolts or screws. FIG. 8Aillustrates a row having three header connectors 805 a, 805 b on eachheader tube 810 a, 810 b, respectively. Other embodiments may includefewer or more header connectors. For example, more header connectors maybe used to reduce the pressure differential.

FIG. 8C is a cross-sectional view of a flat tube 801 of the row of theheat exchanger of FIGS. 8A and 8B taken along section line 8C-8C of FIG.8B. The flat tube 801 includes five channels 820. Other embodiments ofthe flat tube 801 may include fewer or more channels 820. For example,the flat tube 801 may include one channel, two channels, three channels,or six channels.

FIGS. 9A and 9B illustrate heat exchanger fins 905 provided inaccordance with some embodiments of this disclosure. The fins 905 aredisposed between the flat tubes 801 illustrated in FIGS. 8A-8C toincrease heat transfer between the air flowing through the row of theheat exchanger and the fluid, e.g., single-phase fluid, flowing throughthe heat exchanger.

FIG. 10A is a detailed front view of the heat exchanger fins of FIGS. 9Aand 9B in accordance with some embodiments of this disclosure. FIG. 10Bis a cross-sectional view of a heat exchanger fin of FIG. 10A takenalong section line 10B-10B of FIG. 10A. The fin includes a linearportion 1005 and a wave portion 1010, which, in the illustratedembodiment, has a saw-tooth pattern or shape. In other embodiments, thewave portion 1010 may have a sine pattern or a triangular pattern.

FIGS. 11A-11D illustrate yet another heat exchanger provided inaccordance with other embodiments of the present disclosure. As shown inFIG. 11A, the heat exchanger 1100 includes four rows 1101-1104. Row 1101includes header tube 1111 and header connector 1121 attached orconnected together, e.g., by a brazing process. Row 1102 includes firstheader tube 1112 a and first header connector 1122 a connected together,and second header tube 1112 b and second header connector 1122 bconnected together. Row 1103 includes first header tube 1113 a and firstheader connector 1123 a connected together, and second header tube 1113b and second header connector 1123 b connected together. Row 1104includes header tube 1114 b and header connector 1124 connectedtogether. Row 1102 and row 1103 are connected together by connectingheader connectors 1122 a and 1123 a. For example, as illustrated in FIG.11B, header connector 1123 a includes holes or openings 1143 a, 1144 aand header connector 1122 a includes corresponding holes through which abolt or other similar fastener may be placed to connect the headerconnectors 1122 a, 1123 a together. An O-ring or gasket 1105 may beplaced between the header connectors 1122 a, 1123 a to provide a sealagainst leakage of fluid from inside the rows 1101-1104 to the airside.Similarly, header connectors 1121 and 1122 b are connected together andheader connectors 1123 b and 1124 are connected together.

As shown in FIG. 11C, the first header tube 1111 a of the first row 1101includes an inlet connector or tube stub 1141 for connecting to a fluidsupply line and the fourth header tube 1114 a of the fourth row 1104includes an outlet connector or tube stub 1142 for connecting to a fluidreturn line.

Compared to regular fin copper-tube coils, embodiments of the heatexchanger of FIGS. 8A-11D have a lower pressure drop on both the airside and the liquid side. And its high effectiveness results in a smalltemperature approach between the air side and the liquid side.

FIG. 12 is a flow diagram illustrating a process according toembodiments of the present disclosure. After starting, air is moved froma hot aisle formed by IT racks across flat tubes of a first row of afirst heat exchanger and then across flat tubes of a second row of thefirst heat exchanger, at block 1202. At block 1204, a single-phase fluidis pumped through the first heat exchanger from the first row to thesecond row to transfer heat from the air to the single-phase fluid, andthrough a first channel of a second heat exchanger. At block 1206, acooling water solution is pumped through a second channel of the secondheat exchanger and through flat tubes of a third heat exchanger inthermal communication with outdoor air. Then, the process returns toblock 1202.

FIG. 13 is a flow diagram illustrating a method of manufacturingaccording to embodiments of the present disclosure. After starting,multiple flat tubes and tube connections are brazed in a furnace to forma first row, in block 1302. In block 1304, multiple flat tubes and tubeconnections are brazed in a furnace to form a second row. Fins may alsobe coupled between the multiple flat tubes via a brazing process, suchas an aluminum brazing process. In block 1306, the connections of thefirst row and the second row are connected together via O-rings usingfasteners to form a heat exchanger. Additional rows may be formed in afurnace and connected together to form multi-row heat exchangers, suchas four-row heat exchangers according to embodiments of the presentdisclosure.

In block 1308, the first row is connected to a supply line carryingsingle-phase fluid and, in block 1310, the second row is connected to areturn line carrying single-phase fluid. Then, before ending, the heatexchanger is disposed in air communication with a hot aisle so that hotair flows through the heat exchanger from the second row to the firstrow, in block 1312. That is, the exchanger is oriented in a counter-flowconfiguration. In embodiments of heat exchangers including four rows,the first row is connected to a supply line carrying single-phase fluid,the fourth row is connected to a return line carrying the single-phasefluid, and the four-row heat exchanger is disposed in air communicationwith a hot aisle so that hot air flows through the heat exchanger fromthe fourth row to the first row.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of particular embodiments. It is contemplated that theembodiments of FIGS. 8C, 9, and 10 are not just applicable to the heatexchangers shown in FIG. 8 or 11, but are also applicable to theembodiments shown in FIGS. 5-7.

1-20. (canceled)
 21. A heat exchanger, comprising: a first row includinga first pair of header tubes and a first plurality of flat tubes coupledbetween the first pair of header tubes so that the first plurality offlat tubes are in fluid communication with the first pair of headertubes; a second row including a second pair of header tubes and a secondplurality of flat tubes coupled between the second pair of header tubesso that the second plurality of flat tubes are in fluid communicationwith the second pair of header tubes, a header tube of the first pair ofheader tubes coupled to a header tube of the second pair of header tubeswithout using a brazing process; and a plurality of fins disposedbetween each pair of the first and second plurality of flat tubes. 22.The heat exchanger of claim 21, wherein the first row and the second roware separately constructed using a brazing process.
 23. The heatexchanger of claim 21, wherein the first and second plurality of flattubes each include two channels, three channels, or five channels. 24.The heat exchanger of claim 21, wherein the first and second pluralityof flat tubes are extruded or brazed aluminum tubes.
 25. The heatexchanger of claim 21, wherein each of the plurality of fins include awave pattern in the direction of air flow.
 26. The heat exchanger ofclaim 21, wherein the plurality of fins is a louvered fin.
 27. The heatexchanger of claim 21, further comprising: a fluid inlet coupled to andin fluid communication with the first row; a fluid outlet coupled to andin fluid communication with the second row; and one or more fansconfigured to move hot air through the heat exchanger from the secondrow to the first row.
 28. The system of claim 21, wherein the headertube of the first pair of header tubes is coupled to the header tube ofthe second pair of header tubes by coupling a header connection of theheader tube of the first pair of header tubes to a header connection ofthe header tube of the second pair of header tubes through an 0 ring ora gasket and one or more fasteners.
 29. A method of manufacturing a heatexchanger, comprising: coupling a first plurality of flat tubes betweena first pair of header tubes through a brazing process so that the firstplurality of flat tubes are in fluid communication with the first pairof header tubes; coupling a second plurality of flat tubes between asecond pair of header tubes through a brazing process so that the secondplurality of flat tubes are in fluid communication with the second pairof header tubes; and coupling a first header tube of the first pair ofheader tubes to a second header tube of the second pair of header tubeswithout using a brazing process.
 30. The method of claim 29, furthercomprising coupling the first header tube to the second header tube bycoupling a first header connection of the first header tube to a secondheader connection of the second header tube through an O-ring or agasket.